Slovak teenager Mia Pohankova scored the biggest win of her career Thursday, defeating former champion Naomi Osaka in straight sets to reach the quarterfinals of the Toray Pan Pacific Open in Tokyo.

Pohankova, last year's Wimbledon junior singles champion, overcame an early 2-0 deficit to take the opening set 6-3. The world No. 144, who is ranked a career-high, then held her nerve in a closely contested second set, saving break points in two of her service games before breaking Osaka in the 12th game to seal a 6-3, 7-5 victory in 1 hour, 35 minutes.

The win sends Pohankova into the quarterfinals in her first main-draw appearance at a WTA 500-level tournament. It also matches her best result on the WTA Tour Driven by Mercedes-Benz, marking the fourth time she has reached a tour-level quarterfinal. She will aim to reach her first semifinal when she faces American Alycia Parks next.

Pohankova's victory adds to a series of results that have established her as one of the tour's most promising young talents. Ranked No. 659 this time last year, she won an ITF W75 title early this season and finished runner-up at an ITF W100 event in April. She then reached back-to-back semifinals at the WTA 125 level in September before arriving in Tokyo on the back of two wins at the WTA 1000 Wuhan Open.

After a season-long race, the world's top players converge in the California desert with the WTA's biggest title still to be won.

For Osaka, a three-time finalist in Tokyo who was playing the tournament for the first time since 2022, the defeat marks her third consecutive event without a quarterfinal appearance.